Chain Folding and Unfolding Strucutres of Semicrystalline Polymers Elucidated by Solid-State NMR Spectroscopy

非技术概要：许多商业塑料是由“半结晶聚合物”制成的，即在工业加工时具有结晶能力的长链分子。由于优异的机械性能和热性能，重量轻，制造成本低，它们在我们的日常生活中发挥着重要作用。因此，各种半晶聚合物被广泛应用于包装、纺织品、汽车、飞机零件、能源、生物相容性材料等领域。为了进一步提高半晶聚合物的性能，了解它们在固体状态下的详细结构是必要的，但是，尽管在过去的半个世纪里做出了许多努力，聚合物链的三维分子结构仍然没有得到很好的理解。该项目侧重于对以各种方式结晶和加工的样品中半晶聚合物的分子水平结构的基本理解，并可能导致对商用聚合物材料性能改进的预测。PI将使用新颖的专业光谱技术来探测和理解固态样品中单个聚合物分子的形状。该项目还将包括对研究生和本科生的高级科学培训。他们将体验广泛的聚合物研究，包括聚合物合成，结晶，变形，高级表征和模拟。研究成果将在科学期刊上发表，并由研究人员和学生在国家科学会议上发表。技术概述：聚合物结晶涉及构象变化，从熔体和溶液状态的随机线圈，到体积和单晶的折叠链，典型厚度约为5-20纳米。由动力学驱动的聚合物结晶在晶体习性、片层厚度和结晶度等方面产生独特的特征。已经开发了各种表征工具来揭示分层晶体结构。然而，由于实验分辨率的限制，对分子水平构象的理解仍然具有挑战性。PI将采用13C-13C双量子（DQ）核磁共振结合选择性同位素13C标记的新方法来阐明折叠链的再进入位点、连续折叠数和半晶聚合物的相邻再进入部分，包括聚乙烯、等规聚丙烯、等规聚（1-丁烯）和聚（乳酸）在散装和单晶中作为熔体过冷的函数。这项工作旨在提供半结晶聚合物在结晶和变形过程中的详细分子图像，以及与计算机模拟结果的关系，并将增强我们对聚合物材料结晶的理论认识。

NON-TECHNICAL SUMMARY:Many commercial plastics are made of "semicrystalline polymers", i.e. long-chain molecules that have the ability to crystallize when processed industrially. They play important roles in our daily lives due to excellent mechanical and thermal properties, lightness, and easy low-cost fabrication. Thus, various semicrystalline polymers are used in a wide variety of applications including packaging, textiles, automobile, airplane parts, energy, biocompatible materials, and so on. To further improve properties of semicrystalline polymers, understanding of their detailed structure in the solid state is necessary, but, despite many efforts over the last half century, the three-dimensional molecular structures of the polymer chains are still not well understood. This project focuses on fundamental understanding of molecular-level structures of semicrystalline polymers in samples crystallized and processed in various ways, and may lead to predictions of improved properties for commercially available polymeric materials. The PI will be using novel specialized spectroscopic techniques to probe and understand the shapes of individual polymer molecules in the solid-state samples. This project will also include advanced scientific training of graduate and undergraduate students. They will experience a wide range of polymer research covering polymer synthesis, crystallization, deformation, advanced characterizations, and simulations. The research results will be reported in scientific journals and presented by the researcher and students at national scientific meetings.TECHNICAL SUMMARY:Polymer crystallization involves conformational changes from random coils in the melt and solution states, to folded chains in the bulk and in single crystals with a typical thickness of ca. 5-20 nm. The crystallization of polymers driven by kinetics yields unique features in terms of crystal habits, lamellae thickness, and crystallinity, among other features. Various characterization tools have been developed to reveal hierarchical crystalline structures. Nevertheless, the understanding of the molecular-level conformations remains challenging due to limitations of experimental resolutions. The PI will employ a novel approach of 13C-13C double quantum (DQ) NMR combined with selective isotopic 13C labeling to elucidate re-entrance sites of folded chains, successive folding numbers, and adjacent re-entry fractions of semicrystalline polymers, including polyethylene, isotactic polypropylene, isotactic poly(1-butene), and poly(lactic acid) in the bulk and in single crystals as a function of undercooling from the melt. This work is aimed at providing detailed molecular pictures of semicrystalline polymers during crystallization as well as under deformation, in relation also to computer simulation results, and will enhance our theoretical understanding of the crystallization of polymeric materials.